Inhomogenuous Superconductivity Coexisting with SDW stripes in the Two-Dimensional Hubbard Model
Mitake Miyazaki, Kunihiko Yamaji, Takashi Yanagisawa
Nanoelectronics Research Institute, AIST Tsukuba Central 2, Tsukuba 305-8568, Japan
The superconducting and SDW condensation energy of a spatially inhomogeneous d-wave superconducting state coexisting with SDW stripes is studied by using the Variational Monte Carlo method. We calculate its size dependence for various doping rates in the two-dimensional Hubbard model. In the strong correlation system with on-site coulomb energy U=8t, it turns out that the coexistent state is more stable than the commensurate SDW or the homogeneous superconducting state in the under-doping region. The obtained hole-density dependence of the incommensurability of the coexisting state is in good agreement with the neutron scattering data for La2-xSrxCuO4. We also study on CDW amplitude, next-nearest hopping t' and transfer anisotropy.
Unambiguous relationship between the Hubbard, t-J and d-p Models in One-dimension Based on the Luttinger Liquid Theory
Kazuhiro Sanoa, Yoshiaki ¯Onob
a Department of Physics Engineering, Mie University, Tsu, Mie 514-8507, Japan
b Department of Physics, Nagoya University, Nagoya 464-8602, Japan
We examine the one-dimensional (1D) d-p model in comparison with typical 1D models such as the 1D Hubbard model and the 1D t-J model using the numerical diagonalization method combined with the Luttinger liquid theory. We calculate the spin velocity vs, the charge velocity vc and the Luttinger liquid parameter Kr for each model. Using these parameters, a relationship between the models is obtained unambiguously. We find that the d-p model can be described by the Hubbard model in the wide parameter region, while it can be described by the t-J model only in the strong coupling limit.
Strong Evidence for the Three-Dimensional Fermi Liquid Behaviour of Quasiparticles in High-TC Cupurates
Setsuo Misawa
Institute of Quantum Science,Nihon University,Kanda-Surugadai,Tokyo 101-8308,Japan
It is generally believed that the behaviours of quasiparticles (holes) in high-TC cupurates should be attributed to the two-dimensional(2D) electronic states in the Cu-O planes. The various anomalies of the transport coefficients for temperatures above TC are long-standing insoluble puzzles and cause serious controversy. Here we reanalyzed the published experimental data of LSCO cupurates. We have found that the normal-state susceptibility, resistivity, Hall coefficient etc vary precisely as T2lnT as a function of temperature T in agreement with the prediction of the Fermi liquid model. The quasiparticles are shown to definitely behave as a 3D Fermi liquid. Various attempts to describe the system in terms of non-Fermi liquids, e.g. RVB state, seems to be erroneous.
BCS-like Pairing Ground State on Two-Dimensional Plaquette Lattice
Hsiu-Hau Lin, Ming-Shyang Chang
Department of Physics, National Tsing-Hua University, Hsinchu 300, Taiwan, Republic of China
We study the two-dimensional Hubbard model on the plaquette lattice as shown in the figure. At half filling, we solve the ground state exactly in the plaquette limit, tp/t << 1. We are able to put down the exact wave function and determine the symmetry of these preformed pairs. It is rather surprising that the ground state is a spin liquid with preformed BCS-like electron pairs. Upon doping, these preformed pairs are no longer locked to the lattice and become mobile. The ground state changes into a superconductor. Applications for the similar technique to quasi-one-dimensional systems, such as ladders, carbon nanotubes and ribbons, are also discussed.
Parameter Dependence of the Superconducting Condensation Energy of the Two-Dimensional Hubbard Model
Kunihiko Yamaji, Mitake Miyazaki, Takashi Yanagisawa
Nanoelectronics Research Institute, AIST Tsukuba Central 2, Tsukuba 305-8568, Japan
The two-dimensional Hubbard model is believed to contain essential electronic elements which give rise to the high-Tc superconductivity. The strongest material-dependence giving rise to a wide range of Tc must have been condensed in the second nearest neighbor transfer energy t¢. Its evaluation and how and to what extent it enhances superconductivity stay important issues. Using the variational Monte Carlo method we have computed the t¢-dependence of the superconducting condensation energy for the titled model of the size up to 20 ×20 with electron density ~ 0.84. The energy starts to sharply rise when t¢ decreases from zero to -0.10, reaching the maximum around -0.10 ~ -0.15 and turns to decrease, vanishing around -0.35 (in energy unit t). The rising part is in a qualitative agreement with observations.
Spectral properties of incommensurate CDW scattering in cuprates
G. Seibold, S. Varlamov
Institut für Physik, BTU Cottbus, P.O. Box 101344, 03013 Cottbus, Germany
Recent STM experiments strongly support the existence of two-dimensional 'checkerboard' charge modulations in Bi2Sr2CaCu2O8+d. We show that the associated collective charge dynamics can also account for the peculiar features as seen in ARPES experiments. Especially the famous peak-dip hump structure of the line shape and the related kink in the dispersion can be well described by the coupling of the charge carriers to dynamical incommensurate CDW fluctuations. From a comparison with ARPES data we obtain a mode frequency which decreases towards optimal doping thus strongly supporting the existence of a quantum critical point around this concentration. Finally we extend our approach in order to include the recently observed bilayer splitting. It turns out that the coupling to incommensurate CDW modes naturally can account for the reduced splitting in the superconducting state.
Topological order in Gutzwiller-projected wave functions
Dmitri A. Ivanova, T. Senthilb
aInstitute for Theoretical Physics, ETH-Hönggerberg, CH-8093 Zürich, Switzerland
bMassachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge 02139, USA
Gutzwiller projection allows a construction of an assortment of variational wave functions for strongly correlated systems. For quantum spin S = 1/2 models, Gutzwiller-projected wave functions have resonating-valence-bond structure and may represent states with topological order and with fractional quantum numbers for the excitations. Using insights obtained from field-theoretical descriptions of fractionalization in two dimensions, we construct candidate wave functions of fractionalized states by projecting specific superconducting states. We explicitly demonstrate the presence of topological order in these states.
Effect of a geometrical frustration in the doped Mott insulator
Takashi Koretsune, Masao Ogata
Department of Physics, University of Tokyo, Tokyo 113-0033, Japan
The two-dimensional t-J model on the triangular lattice has been studied using high temperature expansions. By calculating the entropy and the spin-spin correlation function through twelfth order in inverse temperature, we revealed that hole doping favors a nearest-neighbor singlet formation, indicating that the resonating valence bond state is stabilized in low temperatures. On the contrary, with electron doping, we find that there exists a wide ferromagnetic region in the phase diagram, which is related to the Nagaoka's ferromagnetism, the flat band ferromagnetism and the Kanamori's ferromagnetism. It is also found that the competition between this ferromagnetic behavior and the antiferromagnetic coupling results in the large effective mass near half filling.
Zero-energy edge states and their origin in particle-hole symmetric systems: symmetry and topology
Shinsei Ryua, Yasuhiro Hatsugaib
a Dept. of Applied Physics, Univ. of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, JAPAN
b Dept. of Applied Physics, Univ. of Tokyo and PRESTO, JST, 7-3-1 Hongo, Bunkyo-ku, Tokyo, JAPAN
When a bulk system is truncated, it may support zero-energy edge states localized near the boundary. In this article, we propose a criterion to determine the existence of zero-energy edge states for a class of particle-hole symmetric systems. A loop is assigned for each system, and its topology and a symmetry play an essential role. Applications to several systems such as d-wave superconductors and graphite ribbons are demonstrated. A variants of the Jahn-Teller theorem for systems with edges is obtained, which we apply to coexistence of different order parameters near the edges in d-wave superconductors.
27Al-Knight Shift Measurement on Heavy-Fermion Superconductor UNi2Al3
K Ishida*a, H Tou **a, Y Kitaokaa, N Tateiwaa, N.K Satob, N Asoc, C Geibeld, F Steglichd
aDepartment of Physical Science, Osaka Univ., Toyonaka, Osaka 560-8531, Japan
bDeptartment of Physics, Nagoya Univ., Nagoya 464-8602, Japan
cNeutron Scat. Lab., ISSP, Univ. of Tokyo, Ibaraki 319-1106, Japan
dMPI for Chemical Physics of Solids, D-01187 Dresden, Germany
We report 27Al Knight-shift (27K) measurement on a single-crystal UNi2Al3 that reveals a coexistence of superconductivity and a SDW type of magnetic ordering (TSDW=4.5 K). The spin part of 27K does not change down to 50 mK across Tc ~ 0.9 K. The behavior of 27K reveals that UNi2Al3 belongs to a class of spin-triplet SC pairing state superconductor like UPt3 and Sr2RuO4.
*Present address: Dept. of Phys. Kyoto Univ. Kyoto 606-8502, Japan. **Present address:ADSM, Hiroshima Univ., Higashi-Hiroshima 739-8526, Japan
Fermi Surface of Ferromagnetic Superconductor URhGe
Hiroshi Yamagamia, Dai Aokib
aFaculty of Science, Kyoto Sangyo University, Kyoto, 603-8555, Japan
bDRFMC-SPSMS, CEA, 38054 Grenoble, France
A discovery of superconductivity at ambient pressure in the ferromagnet URhGe was reported recently. The Curie temperature is 9.5K and the ordered magnetic moment orients along the c axis. URhGe has an orthormbic crystal structure containing zigzag chains of nearest-neighbor uranium ions, which is similar to that of ferromagnetic pressure-induced superconductor UGe2. For investigating a similarity of URhGe and UGe2 in the Fermi surface, all-electron band calculations for ferromagnet URhGe are performed using a fully-relativistic spin-polarized LAPW method within exchange-correlation potentials in a local spin-density approximation. The shape of Fermi surface for URhGe, the contribution of the 5f electrons and the spin-polarization on the Fermi surface are shown as compared with those of UGe2.
Josephson Effect in Heavy-Fermion Superconductor CeTIn5 (T=Co, Ir)
Akihiko Sumiyamaa, Daisuke Katayamaa, Rinpei Hataa, Yasukage Odaa, Yoshihiko Inadab, Dai Aokib, Yoshihumi Tokiwab, Yoshinori Hagac, Yoshichika ¯Onukib
aDepartment of Material Science, Faculty of Science, Himeji Institute of Technology, Ak¯o-gun 678-1297, Japan
bGraduate School of Science, Osaka University, Toyonaka 560-0043, Japan
cAdvanced Science Research Center, Japan Atomic Energy Research Institute, Tokai 319-1106, Japan
The Josephson effect between a single crystal CeTIn5 (T=Co, Ir) and an s-wave superconductor has been investigated for CeTIn5-Cu-Nb junctions. Josephson critical current Ic is observed just below superconducting transition temperature Tc for CeCoIn5, while the temperature below which Ic appears varies from junction to junction and Ic rises gradually at first for CeIrIn5, probably reflecting a distribution of the local transition temperature in CeIrIn5.
NMR/NQR study of CeCoIn5
Yu Kawasakia, Shinji Kawasakia, Takeshi Mitob, Guo-qing Zhenga, Yoshio Kitaokaa, Kenji Ishidac, Hiroaki Shishidod, Rikio Settaid, Yoshinori Hagae, Yoshichika ¯Onukid
aGrad. School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
bFaculty of Science, Kobe University, Kobe, Hyogo 657-8501, Japan
cGrad. School of Science, Kyoto University, Kyoto 606-8502, Japan
dGrad. School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan
eAdv. Sci. Res. Cntr, Japan Atomic Energy Res. Inst., Tokai, Ibaraki 319-1195, Japan
CeCoIn5 is the newly discovered heavy-fermion superconductor with Tc = 2.3 K. In order to investigate the characteristics of spin fluctuations, we have performed In-NQR and Co-NMR experiments on single crystals of CeCoIn5. Our result indicates that the compound is located very close to a magnetic instability by anisotropic antiferromagnetic spin fluctuations.
Fermi surface of the Filled Skutterudite LaOs4Sb12
Hisatomo Harimaa, Katsuhiko Takegaharab
a The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka 567-0047, Japan
b Dept. of Materials Science and Technology, Hirosaki University, Hirosaki, Aomori 036-8561, Japan
The electronic bandstructure and Fermi surface (FS) are calculated for LaOs4Sb12, which is a reference system of a new heavy fermion superconductor PrOs4Sb12. 1 The calculated FS consists of two closed hole surfaces around the G point and a multiply connected one. The recent dHvA measurement for PrOs4Sb12 2 has shown good agreement with the closed FSs topology. The mass enhancement for the cyclotron masses is estimated to be about 5, much less than 10 expected from the specific heat measurement. It indicates the multiply connected FS becomes very heavy superconducting states.
Effect of Phenidone Adsorption on the Superconducting Parameters of Ceramics Bi-Pb-Sr-Ca-Cu-O
Lev L. Makarshina, Valentin S. Kravchenkob, Valentin N. Parmona
aBoreskov Institute of Catalysis, pr. ak. Lavrentieva 5 630090 Novosibirsk, Russia
bInstitute of Inorganic Chemistry, pr. ak. Lavrentieva 3 630090 Novosibirsk, Russia
A treatment of the Bi1.8Pb0.3Sr3-xCa1+xCu3Oz ceramics with acetone solution of phenidone (1-phenyl-3-pyrazoline) at room temperature during 50 days resulted in: (1) for the ceramics with an optimal x, we have observed a two-fold increase in critical current, (2) a high-temperature superconducting phase (with Tc = 105 K) appears in the strontium rich ceramics which was originally nonsuperconducting above 77,4 K, (3) the interaction between phenidone and the ceramics surface results in an increase in the size of a unit cell caused by evolution of labile oxygen due to oxidation of phenidone.
A Comparative Analysis of the Superconducting and Normal-State Properties in Tl2Ba2Can-1CunO2n+4 with Different n
Marina V. Elizarova, Vitaliy E. Gasumyants
St. Petersburg State Technical University, 195251, St. Petersburg, Russia
We have studied the effect of increasing number of copper-oxygen layers on the band spectrum parameters in the normal state for the Tl2Ba2Can-1CunO2n+4 system (n=1,2,3) based on the thermopower analysis within a narrow-band model. The conduction band band is found to be slightly asymmetric, the total effective bandwidth for all the phases with n £ 3 is about 100 meV and demonstrates a tendency to a band broadening with increasing n that correlates with optimization of superconducting properties. The results obtained allowed us to propose an hypothesis for the Tc variation with n in the case of near-optimally doped compositions. This can provide an important information on the nature of the band responsible for the conduction process and on the relation between the normal state and superconducting properties.
Pressure effects on the superconductivity in FeSr2YCu2O7+d oxide superconductor
Hiroaki Hamadaa, Tomohiro Shibataa, Yuh Yamadaa, Shugo Kuboa, Akiyuki Matsushitab
aDepartment of Materials Science, Shimane University, 1060 Nishikawatsu, Matsue 690-8504, Japan
bNational Research Institute for Metals, 1-2-1 Sengen, Tsukuba 305-0047, Japan
We have investigated the pressure dependence of superconducting transition temperature (Tc) in FeSr2YCu2O7+d oxide superconductor (Fe1212). The superconducting Fe1212 samples were synthesized by solid-state reaction with multiple annealing process. The Tc-onset of this sample exhibited about 60 K at an ambient pressure. The pressure dependence of Tc was obtained about 2.1 K/GPa up to 2 GPa.
Partial Melting in Filamentary Sm-Ba-Cu-O Superconductors
under Various Oxygen Atmospheres
Eriko Bana, Tomoko Gotob, Yoshiharu Matsuokaa
aMeijo University, 1-501 Shiogamaguchi, Tenpaku-ku, Nagoya 468-8502, Japan
bNagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 465-8555, Japan
The filamentary Sm123 precursor was prepared by a solution spinning method. The precursor was partially melted in flowing 0.1%O2+Ar and 1%O2+Ar and oxygenated. The obtained sample showed the Tc value of around 90 K and exhibited dense and well aligned texture along the filament diameter as well as the direction of filament length. The sample melted in flowing 1%O2+Ar showed a relatively high Jc value more than 104A/cm2 over a wide partial melting temperature range of 1020°C-1050°C and the excellent reproducibility.
Critical temperature oscillation in the thermal cycle below 16 K
in Y0.83Ca0.17Ba2Cu3O6 sintered sample
Tatsuya Honmaa, Pei Herng Horb, Mitsuho Tanimotoa
aDept. of Physics, Asahikawa Medical College, Midorigaoka-Higashi 2-1-1-1, Asahikawa 078-8502, Japan.
bDept. of Physics, and Texas Center for Superconductivity, Univ. of Houston, Houston, TX77004, U.S.A.
We report the evolution of a three-step incipient resistive superconducting transition in Y0.83Ca0.17Ba2Cu3O6 sintered sample under high pressure. The superconductivity shows the relaxation effect in the loading and unloading process below 0.4 GPa. After quenching the sample under the relaxation process below 80 K, significant oscillation of the resistive superconducting transition is observed in the thermal cycle below ~ 16 K, in spite of no change in the normal-state resistivity. Since there is no mobile oxygen in the present sample, the effect of oxygen rearrangement can be ignored. The observed result will be discussed by the pressure-induced Josephson coupling and charge redistribution within the CuO2 planes.
Depression of the Superconducting Transition Temperature of La2CuO4+d by Neutron Irradiation
Koh-ichi Uedaa, Takao Koharaa, Moritami Okadab, Hisao Kodakab, Kiyomi Miyatab, Satoshi Watauchic, Isao Tanakac
aDiv. of Mater. Sci., Grad. School of Sci., Himeji Inst. of Tech., Kamigori-cho, Hyogo 678-1297, Japan
bResearch Reactor Institute, Kyoto University, Kumatori-cho, Osaka 590-0494, Japan
cFaculty of Engineering, Yamanashi University, Kofu, Yamanashi 400-8511, Japan
The aim of this work is to investigate the influence of neutron irradiation to superconductivity of the oxygen loaded La2CuO4+d, which were prepared from one single crystal of La2CuO4. The excess oxygen was loaded by annealing under high pressure oxygen gas. The neutron irradiation were performed at 10 K in the low temperature irradiation facility of Kyoto University Reactor. As a result, there were no signs of the raise of Tc. The depression rate of Tc by the irradiation is about -1K/1017n/cm2.
Magnetic Flux Penetration in the Superconducting Core of Bi-2223 Tape
Alexey V. Pan, Shixue Dou, Huakun Liu
Institute for Superconducting and Electronic Materials, University of Wollongong, Northfields avenue, Wollongong, NSW 2522, Australia
Magnetic flux penetration into the superconducting core of Bi-2223 tapes is overlooked. Upon increasing magnetic field Ba applied perpendicular to the main tape plane, the ``local" magneto-optical imaging shows that the flux penetrates in the core starting from its edges: first, filling regions in between grains, which are 5-30 mm large. As soon as magnetic flux has filled the regions around the grains throughout the entire core at B*a @ 15 mT (T = 15 K), a decrease in the critical current density Jc(Ba) measured separately by ``global" magnetization measurements is observed. Below this field B*a, the Jc(Ba) behavior exhibits a magnetic filed independent plateau often referred to the single vortex pinning regime. The origin of the ``global" Jc plateau discussed in the frame of the ``local" flux penetration observed.
(119) BSCCO superconducting films synthesized by MOCVD on vicinal (110) SrTiO3
K. Endo, P. Badica, T. Yoshizawa, K. Abe, J. Itoh
NeRi, AIST Tsukuba Central 2, 1-1-1 Umezono, 305-8568 Japan
(119) Bi-2223 superconducting thin films have been synthesized by MOCVD. The substrate was vicinal (110) SrTiO3 with the off-angles along [110] azimuth of 10-20 degrees. As-synthesized films have been characterized by AFM and resistivity measurements versus temperature. Higher critical temperatures Tco and growth with less twins was observed for the films synthesized on the substrates with higher off-angles.
Local Magnetic Properties of High-Tc Superconductors Probed by Scanning SQUID Microscopy
Junpei Kasaia, Noriaki Okazakia, Yoshihiko Togawab, Jun-ichi Shimoyamab, Kohji Kishiob, Makoto Ohtanic, Tomoteru Fukumurac, Masashi Kawasakic, Hideomi Koinumaa, Tetsuya Hasegawaa
aMaterials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan
bDepartment of Superconductivity, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
cInstitute for Materials Reaserch, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
In order to investigate the local magnetic properties in high-Tc superconductors, we have performed scanning SQUID microscopy on the ab-surfaces of La2-xSrxCuO4 and Bi2Sr2CaCu2Oy single crystal at various temperatures. The observed magnetic images demonstrated the spatial variations of Tc, which are strongly correlated with the vortex distribution.
Grain orientation of YBa2Cu3Ox high-Tc superconductors studied by OIM
A. Koblischka-Venevaa, M. R. Koblischkab
aInstitute for Functional Materials, P.O. Box 151150, D-66041 Saarbrücken, Germany
bInstitute of Experimental Physics, P.O. Box 151150, D-66041 Saarbrücken, Germany
Orientation imaging microscopy (OIM) provides a method for measuring a large number of individual grain orientations and relating them directly to the microstructural features by means of evaluating electron backscatter Kikuchi patterns in scanning electron microscopy. We investigated the grain orientation distributions of various YBCO ceramic samples prepared with different Alkali metal additions. The samples are characterized by pole figures, inverse pole figures, and grain orientation maps. Grain orientation distribution functions are obtained from the measured data. The KClO3-doped samples are shown to exhibit a texture for an addition in the initial batch between 3 and 5 wt.-%. This observation explains the increased critical current density in the doped samples.
Superconducting Gap and Pseudogap in Bi2Sr2Ca2Cu3O10+d by Short-Pulse Interlayer Tunneling Spectroscopy
Yoshiharu Yamadaa, Kenkichi Anagawaa, Takenori Fujiib, Takao Watanabeb, Azusa Matsudab, Takasada Shibauchia, Minoru Suzukia
aDepartment of Electronic Science and Engineering, Kyoto University, Kyoto 606-8501, Japan
bNTT Basic Research Laboratories, 3-1, Morinosato Wakamiya, Atsugi-shi, Kanagawa 243-0198, Japan
We have measured the superconducting gap, pseudogap and their doping dependence of trilayer high-Tc superconductor Bi2Sr2Ca2Cu3O10+d by short-pulse interlayer tunneling spectroscopy. It is found while both gaps are a little larger than those of the bilayer system and exhibit similar temperture dependence, their systematic doping dependence has revealed an anomalous relationship between Tc and the gap size, i.e., in the overdoped region, Tc does not change from its optimum value while the gap decreases with doping. This suggests that inequivalent hole doping occurs, which is supposed in multilayer systems.
Intrinsic tunneling: a look from inside on high Tc superconductors.
Vladimir M. Krasnov
MINA, Chalmers University of Technology, SE-41296, Göteborg, Sweden
Layered structure of high Tc superconductor, provides a unique opportunity to probe quasiparticle density of states inside a bulk single crystal by means of interlayer tunnelling. Here I present a systematic doping, temperature and magnetic field dependent intrinsic tunneling spectroscopy of Bi-2212. An improved resolution made it possible to simultaneously trace the superconducting gap (SG) and the pseudo-gap (PG) in a close vicinity of Tc and to analyze closing of the PG at T*. The obtained doping phase diagram exhibits a critical doping point for the PG and a characteristic crossing of the SG and the PG close to the optimal doping. This points towards coexistence of two different and competing order parameters in Bi-2212. Experimental data indicate that the SG can form a combined (large) gap with the PG at T < Tc and that the interlayer tunneling becomes progressively incoherent with decreasing doping.
STM/STS study on Ca2-xNaxCuO2Cl2 single crystals
Y. Kohsakaa, T. Hanaguria, K. Kitazawaa, M. Azumab, M. Takanob, H. Takagia
aDepartment of Advanced Materials Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
bInstitute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611-0011, Japan
To explore the evolution of electronic states from the Mott insulator to the high-Tc superconductor, we performed scanning tunneling microscopy/spectroscopy (STM/STS) on Ca2-xNaxCuO2Cl2 (x ~ 0.08) single crystals which show superior cleavage. Topographic images at 7 K show clear atomic images superposed on nano-scale patch-like or river-like irregular corrugations. Spectroscopic measurements revealed that low areas are semiconducting. In high areas, the density of state (DOS) near Fermi level (EF) increases and DOS at EF becomes finite, while gap-like feature ( ~ 100 meV) still remains. Namely, background corrugations are originated from the electronic inhomogeneity.
Fluctuation Conductivity of Polycrystalline Hg,Tl-1223
Shun-Hui Hanab, Johan Axnäsb, Ingrid Bryntsec, Bairu Zhaoa, Östen Rappb
aNational Laboratory for Superconductivity,Institute of Physics, CAS, P.O.Box 603, Beijing,100080,CHINA
bSolid State Physics, IMIT, KTH Electrum 229, SE-164 40 Stockholm-Kista, SWEDEN
cInorganic Chemistry, Arrhenius Laboratory, Stockholm University, SE-106 91 Stockholm, SWEDEN
Detailed resistivity measurements were made for polycrystalline Hg1-xTlxBa2Ca2Cu3O8+d with x = 0 and 0.2 in zero applied magnetic field and above the superconducting transition Tc. The fluctuation conductivity Ds is analyzed. Two crossover temperatures, T* (from two to three dimensional fluctuations in the mean field region (MFR)) and TG (from the MFR to the critical region) could be identified for each sample. All results are in agreement with the Lawrence-Doniach model. The c-axis coherence length and the interlayer coupling factor are obtainned. The choice of background resistivity and the pseudo-gap effect on Ds are discussed.
Evidences of Static Stripe Order in (RE)Ba2Cu3O6+x Compounds
Fedor N. Bukhanko, Nikolay A. Doroshenko, Victor I. Kamenev
Donetsk Inst. of Physics and Technology, Donetsk, 83114, Ukraine
We have recently revealed that a stabilization of the orthorhombic crystal superstructure with 2a lattice period (Tc=50K) in the (RE)Ba2Cu3O6+x compounds takes place at 300K within narrow interval 0,45<x<0,65 and one is accompanied by jump of lattice parameter c and appearance of a plateau in the concentration dependences of electronic,magnetic and structural ptoperties versus x,connected evidently with pinning of dynamical stripe order of holes in CuO2 layers with the hole concentration per Cu p=1/8 for x=0,5.We assume that 2a superstructure makes stripe order static,because this crystal structure is commensurable with period of the dynamic 1D space modulated spin-charge structures in the CuO2 layers.
AC Susceptibilites in Ag-based Hg(Pb,Bi)-1223 Superonductors
Nobuyoshi Sakamotoa, Tadahiro Akunea, Hamid R. Khanb, Klaus Lüdersc
aDept. of Electr. Enginr., Kyushu Sangyo University, 2-3-1 Matsukadai, 813-8503 Fukuoka, Japan
bFEM, Katharinenstr.17, D-73525 Schwäbisch Gmünd, Germany
cInstitut für Experimentalphysik, Freie Universität Berlin, Arnimallee14,D-14195 Berlin, Germany
Compounds of the Hg1-xPbxBa2CaCu3O8+d (x=0.1 and 0.2) and Agy(HgBa1.9Bi0.1Ca2Cu3O8+d)1-y (y=0.1 and 0.2) were synthesized directly from the metal oxides without using a precursor. The structural and morphological properties were investigated. AC susceptibilities and DC magnetizations were measured using a SQUID magnetometer and a PPMS susceptometer. From the magnetic data, the critical temperatures are 131K in the composites and the estimated superconducting volume reduces when Ag content increases. Critical current deinsities estimated from the magnetization. AC losses were estimated from the imaginary part of the AC susceptibilities c¢¢ and favorably compared with the Bean model.
The coexistence of magnetism and superconductivity in HgBa2Ca4Cu5Oy :
63Cu-NMR Study
Hisashi Kotegawaa, Yo Tokunagaa, Kenji Ishidaa, Yoshio Kitaokaa, Ken Itohb, Kazuyasu Tokiwab, Tuneo Watanabeb, Akira Iyoc, Hijiri Kitoc, Yasumoto Tanakac, Hideo Iharac
aGraduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
bDepartment of Applied Electronics, Science University of Tokyo, yamazaki, Noda, Chiba, Japan
cNational Institute of Advanced Industrial Science and Technology (AIST), Umezono, Tsukuba, Japan
We report NMR study on five-layered HgBa2Ca4Cu5Oy with Tc=110 K. Knight shift at 63Cu site indicates that the outer pyramidal CuO2 planes are optimally doped, while inner planar ones are significantly underdoped. The signal of the inner planes disappear below ~ 150 K due to the strong antiferromagnetic spin correlations. Nuclear spin-lattice relaxation rate, 1/T1 at the outer planes suggests that antiferromagnetic order occurs in the inner planes at ~ 60 K.
Strongly Correlated Superconductivity close to Mott Insulators
Massimo Caponea, Michele Fabriziob, Erio Tosattib, Claudio Castellania
aUniversity of Rome "La Sapienza", and INFM, SMC Center, Department of Physics, Piazzale Aldo Moro, 2, I-00185, Rome,Italy
bInternational School for Advanced Studies (SISSA-ISAS) and INFM, Via Beirut 2-4, I-34013, Trieste and ICTP, P.O. Box 586, I-34014 Trieste, Italy
High temperature superconductivity in doped Mott insulators like the cuprates contradicts the conventional wisdom that electron correlation opposes to superconductivity. The fullerene, which have recently found to be high-Tc superconductors, are also correlated materials. We examine a dynamical-mean-field solution of a model for electron doped fullerenes which shows how strong correlations can enhance superconductivity close to the Mott transition. We argue that the mechanism responsible for this enhancement could be common to a wider class of models, including those for cuprate superconductors.
The magnitude and temperature dependence of pseudogap in YBCO obtained from resistance measurements
Mikhail P. Volkov, Dmitri D. Prokofiev, Yuri A. Boikov
Ioffe Physicotechnical Institute of RAS, 194021 St. Petersburg, Russia
We report the analysis of the temperature dependence of excess conductivity Ds of the underdoped YBCO epitaxial thin films at temperatures much higher than the superconducting critical temperature Tc. The excess conductivity was determined as the difference of the extrapolated normal resistivity and the measured resistivity. It was found that the temperature dependence of the excess conductivity can de described by the following relation Ds = A (1-T / T *)exp(D*/T). It is proposed that this relation reflects the pseudogap appearance and the magnitude and temperature dependence of the pseudogap were calculated and compared with published experimental and theoretical results.
Observation of quantum tunneling of vortices in MgB2 superconductors
Y. Z. Zhanga, R. Deltourb, H. H. Wena, Z. X. Zhaoa
aNational Laboratory for Superconductivity, Institute of Physics & Centre for Condensed Matter Physics, Chinese Academy of Sciences, P.O. Box 603, Beijing 100080, China
bUniversite Libre de Bruxelles, CP 233, Physique des Solides, B-1050, Brussels, Belgium
Irreversibility lines and magnetic relaxation of MgB2 are studied. The Large separation between irreversibility line and upper critical magnetic field for T® 0 is explained by quantum tunneling of vortices. Theoretical fits are in good agreement with experimental data. A quantum correction of the relaxation rate, followed by a time dependence of the corresponding magnetic moment, is proposed leading to a simple evaluation of the energy barrier: U0(T,H) ~ Uth(T)UH(H) µ (1-T/Tc)a (m0H)b with a ~ 1.5 and b ~ -2.0.
Third harmonic ac susceptibility measurements on MgB2 bulk: irreversibility line and frequency dynamic behaviour
D. Di Gioacchinoa, P. Tripodib, U. Gambardellaa
aI.N.F.N. Frascati National Laboratory, Via Enrico Fermi 40, 00044 Frascati (Italy)
bENEA-Centro ricerche Frascati, Via Enrico Fermi 45, 00044 Frascati (Italy)
The third harmonics of the ac susceptibility of MgB2 high pressure (HP) bulk samples have been measured at the frequency of 1070 Hz as a function of the temperature for different dc magnetic fields. The irreversibility line (IL) has been extracted from their temperature onsets. the IL has a typical Ginsburg-Landau dependence. Others IL lines of HP samples, draw out from VSM measurements at few Hertz, have similar behaviour. This shows that the superconducting response is indipendent from the frequency and the critical state is apply. This analysis supports that the flux dynamic is not induced by the weak link properties and a strong pinning process can be supposed in these materials.
Specific heat and thermal conductivity evidence for two-gap superconductivity in MgB2
A.I. Golovashkina, N.V. Anshukovaa, B.M. Bulichevb, L.I. Ivanovac, A.A. Minakovd, A.P. Rusakovc
aP.N.Lebedev Physical Institute RAS, Moscow, Russia
bMoscow State University, Moscow, Russia
cMoscow Steel and Alloys Institute, Moscow, Russia
dGeneral Physics Institute RAS, Moscow, Russia
Specific heat C(T) and thermal conductivity K(T) for MgB2 were measured in temperature interval T=5-45K. It was found that in addition to known features near the superconducting transition at Tc » 40K there was anomalous behavior both C(T) and K(T) near T » 10K. At the same temperature area the negative thermal expansion of MgB2 was observed earlier. All these anomalies at low temperatures were explained.
Superconductivity of MgB2 wires
Gheorghe Iloncaa, Tzuen Rong Yangb, Aurel Popa, Gabriela Stiufiuca, Ovidiu Furduia
aBabes-Bolyai University, 3400, Cluj Napoca, Romania
bNational Taiwan Norma University, Department of Physics, Taipei, Taiwan, ROC
MgB2 superconducting conductors have been prepared in a cooper sheath by standard powder-in-tube technique. Mg + 2B powder of high purity was ball-milled under argon atmosphere. This mixture was used to fill the cooper metal tubes. Wires were manufactured by the in situ technique, diffusing Mg to B particles, resulting MgB2 with hexagonal structure, after cold deformation. A strong evidence for high intergranular critical current densities and large bulk magnetic flux pinning in superconducting polycrystalline MgB2 has been observed. A comparative study of the intergranular current and grain conductivity was conducted by transport and magnetic susceptibility measurements, in magnetic field up to 7 T to define the Jcmag and the direct current Jc at 4.2 K, which revealed systematic differences in the flux pinning of the wires which is in very good agreement with direct high transport current measurements.The absence of weak link nature in this material has profound a wide range of engineering applications.
Multi-gap structure of the binary superconductor MgB2
Tomoaki Takasakia, Toshikazu Ekinoa, Takahiro Muranakab, Hironobu Fujiia, Jun Akimitsub
aGraduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
bDepartment of Physics, Aoyama-Gakuin University, Setagaya, Tokyo 157-8572, Japan
Tunneling measurement on MgB2 has been carried out with a break junction technique. We have obtained the largest gap of D ~ 9-10 meV with 2D/kBTc ~ 5.3. In addition to this gap, the two-gap structures have been also observed. These two-gap spectra can be fitted by a correlated two-gap model. The fitted parameters vary rather widely leaving the larger gap parameter of ~ 6-7meV kept almost constant.
Fabrication of MgB2 Thin Film by rf Magnetron Sputtering
Soon-Gul Lee, Jong-Rok Ahn
Department of Physics, Korea University, 208 Seochang-dong, Jochiwon, Chungnam 339-800, Republic of Korea
Fabrication of superconducting MgB2 thin film on sapphire substrates by rf magnetron sputtering has been studied. We have tried both single-target sputtering method using an Mg-excessive MgB2 target and co-sputtering of Mg and B. Argon sputtering pressure was 20 mtorr and 5 % of hydrogen gas was added to trap remanant oxygen gas in the deposition chamber. Films were made either by in-situ deposition or in-situ annealing after the room-temperature deposition. While the films by co-sputtering with in-situ annealing showed transition temperatures higher than 24 K, those by single-target sputtering or in-situ cosputtering showed no superconducting transition or very low Tc at best. Details of the fabrication procedures will be dicussed.
Specific Heat of Mg11B2: Evidence for a Second Energy Gap
N. E. Phillipsa, F. Bouqueta, R. A. Fishera, D. G. Hinksb, J. D. Jorgensonb
aLawrence Berkeley National Laboratory, University of California, Berkeley, CA 94720 USA
bMaterials Science Division, Argonne National Laboratory, Argonne, IL 60439 USA
We report measurements of the specific heat of Mg11B2, from 1 to 50 K and in magnetic fields to 9 T, and give the values of parameters relevant to the superconductivity. The superconducting-state electron contribution is dramatically different that of other superconductors, but the general features are consistent with predictions for a two-gap superconductor, and can be quantitatively represented by a two-gap model based on BCS thermodynamics. Parameters characterizing the gaps are in good agreement with some spectroscopic determinations, and also with theoretical calculations. An unusually strong magnetic field dependence of the temperature-proportional term in the electron contribution to the vortex-state specific heat is evidently another manifestation of the two gaps.
Fabrication and critical current density in the single and multifilament MgB2 superconducting wires
Saeid Soltanian, Xiaolin Wang, Aihua Li, Josiph Horvat, E. W. Collings, M. D. Sumption, E. Li, H. K. Liu, S. X. Dou
Institute for Superconducting and Electronic Materials, University of Wollongong, NSW 2522 Australia
The powder in tube method has been used to fabricate Ag, Cu and Fe clad MgB2 wires using an in-situ reaction method. For Ag clad wire Jc is improved by more than two times after the short time sintering process. Jc values of 1.2×105 A/cm2 in zero field and above 104 A/cm2 in 2T at 20 K have been achieved for Ag clad MgB2 wire which is only sintered for 6 minutes at 800oC. Sixteen-filament stainless steel/Fe/MgB2 wires also were fabricated by the powder-in-tube method followed by groove rolling and a short 8min/950oC heat treatment. Magnetic critical current densities of 3.4×105 A/cm2 in 0.5T and about 1.9×105 A/cm2 in 1T at 5 K were achieved.
Anomalous low-temperature thermal conductivity of MgB2
A. V. Sologubenko, J. Jun, S. M. Kazakov, J. Karpinski, H. R. Ott
Laboratorium für Festkörperphysik, ETH Hönggerberg, CH-8093 Zürich, Switzerland
The ab-plane thermal conductivity of single-crystalline MgB2 has been measured as a function of magnetic field with orientations both parallel and perpendicular to the c-axis and at temperatures between 0.5 and 40 K. Applying a magnetic field at constant temperature first leads to a reduction of the lattice thermal conductivity and subsequently to a rapid quasi-logarithmic increase of the electronic thermal conductivity in fields far below the upper critical field Hc2, followed by a saturation at intermediate fields and another rapid increase in the vicinity of Hc2. This behavior is associated with the field-induced suppression of two superconducting energy gaps of significantly different magnitude. At temperatures well below Tc an anomalous nonlinear temperature dependence of the electronic thermal conductivity is observed in the mixed as well as in the normal state.
Vortex Phase Diagram of YBa2Cu4O8 in H||c and H||b
Kazumasa Katayamaa, Takekazu Ishidaa, Seiji Adachib, Setsuko Tajimab
aDepartment of Physics and Electronics, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
bSRL-ISTEC, 10-13 Shinonome 1-chome, Koto-ku, Tokyo 135-0062, Japan
Vortex phase diagram of YBa2Cu4O8 has been investigated by means of the AC susceptibility and the DC magnetization. Phase diagram in H||c is very different from Bi2212 and Y123 because the onset field of the magnetization peak increases rapidly as T decreases at temperatures below 40 K. The AC susceptibility and the DC magnetization measurements in H ||b reveals that the irreversibility line is almost independent of the applied field (at ~ 40 K). We argue that there must be an additional pinning mechanism in YBa2Cu4O8 at temperatures below 40 K compared to Bi2212 and Y123. A possible candidate for pinning centers is a spin density wave which is recently predicted by our group. This work is partially supported by New Energy and Industrial Technology Development Organization (NEDO).
Collective motion of Josephson vortices in Bi2Sr2CaCu2O8+d mesa structures
H.-S. Changa,c, D.-I. Changa, J. Kimb, H.-J. Leea, M.-H. Baea, B.-C. Woob, M. Odad
aDepartment of Physics, Pohang University of Science and Technology, Pohang 790-784, Korea
bElectronic Device Group, Korea Research Institute of Standards and Science, Taejon 305-600, Korea
cMaterial Science Team, Korea Basic Science Institute, Taejon 305-333, Korea
dDepartment of Physics, Hokkaido University, Sapporo 060-0810, Japan
Collective motion of Josephson vortices generated by microwaves or by a dc magnetic field in parallel with the planes of intrinsic junctions of Bi2212 single crystals was studied. In both cases, at a low vortex density and driving current, splitting of the `supercurrent' branch in the current-voltage characteristics (IVC) corresponding to different plasma excitation modes was observed. At a higher vortex density, generated by fields beyond 3-4 T, the IVC merged into a single non-hysteretic curve with kinks, similar to the features caused by the theoretically predicted structural transformation of moving vortex patterns.
Frequency Dependence of the Depinning and Irreversibility Lines in BSCCO
Sozeri Huseyin, Dorosinskii Lev
TUBITAK-UME, National Metrology Institute, PO. Box 54, TR-41470 Gebze/Kocaeli, TURKEY
Penetration of AC magnetic field in Bi2Sr2CaCu2O8+d single crystals was studied using the magnetooptic technique. It was found that the apparent depinning line shifts towards higher (H, T) values with increasing field frequency. At higher frequencies irreversibility in magnetization is controlled by pinning but not by the geometrical or surface barrier. Comparison with the melting line has shown that the depinning line lies completely in the vortex liquid region. Moreover, at least in low DC fields, the vortex liquid does not become unpinned up to the critical temperature of superconductor. Therefore, contrary to general understanding, we show that pinning is the main reason of irreversibility in magnetization at higher frequencies. It was also shown that the reason why this pinning is not observed at lower frequencies ( i.e., using slow measurement technique ) is the giant flux creep in BSCCO.
Preparation, scaling behavior of activation energy, and anisotropy of Hg-1212 HTS thin films
Abouelwafa Salem, Gerhard Jakob, Michael Basset, Hermann Adrian
Institut für Physik, Johannes Gutenberg-Universität, 55099 Mainz, Germany
We have successfully prepared high-quality epitaxial (Hg0.9Re0.1) Ba2CaCu2O6+d HTS thin films without special handling during the preparation. The resistive transition have been investigated in magnetic fields up to 6 T parallel and perpendicular to the c-axis. We have determined the scaling behavior of the effective activation energy. Under variation of the angle q between the field direction and the c-axis of the film with high angular resolution ( Dq » 0.1 °) the anisotropic properties of the vortex state and the depinning field of epitaxially grown Hg-1212 films have been studied.The films exhibit sharp superconducting transitions at Tc @ 120 K with DT @ 2 K. Also the films exhibit critical field anisotropy with a factor 7.67 with respect to the c-axis.
High-field Paramagnetic Meissner Effect in Melt-textured YBCO
Fabio T. Diasa, Paulo Pureura, Pedro Rodrigues Jr.b, Xavier Obradorsc
aInstituto de Fisica, Universidade Federal do Rio Grande do Sul, 91501-970 Porto Alegre, Brazil
bDepartamento de Fisica, UEPG, 84031-510 Ponta Grossa, Brazil
cInstitut de Ciencia de Materials, CSIC, Campus de la UAB, 08193 Bellaterra, Catalunya, Spain
We present systematic field-cooled magnetization measurements in five directionally solidified samples of YBCO containing different amounts of Y-211 precipitates. Fields up to 50 kOe were applied either parallel or perpendicular to the Cu-O atomic planes. Paramagnetic Meissner effect (PME) was observed at high enough fields in all of the studied samples, regardless of the field orientation. This high-field PME shows some noticeable differences when compared to the most frequently investigated low-field PME. Our results are discussed in the light of the existing models for the PME and the role of pinning by Y-211 particles is suggested.
Generation and amplification of the electromagnetic radiation by superconducting films
Alexandre Lykov
P.N.Lebedev Physical Institute of RAS, Leninsky prosp., 53, 119991, Moscow, Russia.
Coherent microwave radiation has been directly detected from Nb and GdBa2Cu3O7-x films in the frequency range up to 600 MHz. The mixed state in the superconducting films has been influenced by a superposition of two alternative magnetic fields directed perpendicular to film surface. First of them, which slow varies in time, sets up the vortex structure in the film. The interaction of the vortices with planar pinning centers leads to a metastable mixed state. While the second high-frequency electromagnetic field either external or emitted by the film, if a feedback is used, provides a synchronization of Abrikosov vortex motion. The simultaneous action of the fields results in either the amplification or generation of electromagnetic radiation. Harmonic mixing of the radiation is also detected.
Order parameter and pseudogap in electron doped high-temperature superconductors
Lambert Alff, Bettina Welter, Yoshiharu Krockenberger, Achim Marx, Rudolf Gross
Walther-Meißner-Institut, Walther-Meißner-Str. 8, 85748 Garching, Germany
Recently, renewed interest in electron-doped high-temperature superconductors (HTS) has arisen from the question whether the phase diagram is symmetric with respect to electron/hole doping. The presently contradictory experimental status in favor of d- or s-wave symmetry of the superconducting order parameter for electron doped HTS is discussed. There are only few experimental reports on the pseudogap behavior of electron doped HTS. Here, we report on the observation of two different kinds of a normal state pseudogap in the electron doped HTS La2-xCexCuO4 and Pr2-xCexCuO4, one on the scale of the superconducting gap energy D, and one on the scale of the magnetic interaction energy J. Both gaps decrease resp. vanish with increased doping.
Magnetic excitations in the spin-glass phase of La2-xSrxCuO4
Hideto Gokaa, Shin-ichi Kuroshimaa, Masaki Fujitaa, Kazuyoshi Yamadaa, Haruhiro Hirakab, Yasuo Endohb, C. D. Frostc
aInstitute for Chemical Research, Kyoto Univeristy, Gokasyo, Uji 611-0011, Japan
bInstitute of Material Research, Tohoku University, Sendai 980-8577
cRutherford Appleton Laboratory, Chilton, Didcot OX11 0QX, United Kingdom
Magnetic excitations of La1.95Sr0.05CuO4 were investigated using pulsed neutron inelastic scattering over a wide range of energy up to 300meV. In contrast to the optimally doped superconductor the dynamical magnetic susceptibility c "(w) around (p,p) in the spin-glass phase monotonically decreases with increasing w and nearly saturates beyond ~ 50meV. We found that the energy dependence of the q-width in the latter energy region is ascribed to a two-dimensional spin-wave dispersion relation with the nearest neighbor interaction J of 108±0.6meV, which is smaller by ~ 20% than that of La2CuO4.
63Cu-NMR study of single-layer high-Tc cuprate Bi2Sr2-xLaxCuO6
Akihiro Sakaia, G.-q. Zhenga, Y. Kitaokaa, C.T. Linb, B. Liangb
aDepartment of Physical Science, Osaka University, Osaka 560-8531, Japan
bMax-Planck-Institut fur Festkorperforschung, Heisenbergstr.1, D-70569 Stuttgart, Germany
We present 63Cu-NMR studies in single crystals of the single-layered high-Tc cuprates Bi2Sr2-xLaxCuO6. In the overdoped sample Bi2Sr2CuO6 (Tc=9 K), we find that the ground state is a Fermi liquid state. We will also present results for under- and optimally-doped samples and discuss the phase diagram of this series of materials.
Anomalous Damping of Phonon Thermal Transport in Slightly Y- or Eu-doped La2CuO4 Single Crystals
X. F. Sun, Seiki Komiya, Yoichi Ando
Central Research Institute of Electric Power Industry, Komae, Tokyo 201-8511, Japan
We found that slight doping (1%) of Y or Eu to the La site strongly suppress the phonon peak at ~ 20 K in the thermal conductivity of La2CuO4. Especially, the phonon peak completely disappears in the in-plane direction and this suppression is much stronger than that observed in 1%-Sr-doped La2CuO4. Magnetic susceptibility measurements show that compared to La2CuO4, apart from nearly unchanged Néel transition around 300 K, there appear some almost-T-independent magnetic moment in Y- or Eu-doped samples. This additional moment may come from the local lattice distortion (which causes incomplete cancellation of the antiparallel Cu2+ spins) or from the magnetic Eu3+ ions. Apparently these local moments strongly scatter phonons, which suggests a strong spin-phonon coupling in the cuprates.
Peculiar Evolution of the c-Axis Charge Transport in La2-xSrxCuO4 Single Crystals from Antiferromagnetic Insulator to Superconducting Regime
Seiki Komiya, Yoichi Ando, X.F. Sun, A.N. Lavrov
Central Research Institute of Elecrtic Power Industory, Komae, Tokyo 201-8511, Japan
The in-plane and the out-of-plane resistivities (rab and rc) are measured in high-quality La2-xSrxCuO4 single crystals in the lightly- to moderately-doped region (x=0.01-0.10). It is found that the resistivity ratio rc/rab at moderate temperatures (100-300 K) is almost completely independent of doping for 0.01 £ x £ 0.05. It is discussed that this striking doping-independence of rc / rab is consistent with the idea that charges form a self-organized network of hole-rich paths, which also explains the unusually metallic in-plane transport in the lightly-doped region [Y. Ando, A.N. Lavrov, S. Komiya, K. Segawa, and X.F. Sun, PRL 87, 017001 (2001)]. For x > 0.05, rc/rab shows a rapid decrease, which suggests that the c-axis charge confinement becomes less effective as x is increased in the superconducting regime.
Low-Temperature Specific Heat of overdoped Bi2201 Single Crystals
Hiroshi Ikutaa, Masaaki Matsuurab, Tetsushi Biwab
aCIRSE, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
bDept. Crystalline Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
Low-temperature specific heat of Pb-doped Bi2Sr2CuO6+d single crystals with various doping states was studied. The most overdoped sample showed no evidence of superconductivity down to 0.5 K, while Tc increased up to 19 K with reducing the oxygen content. The specific heat included a linear-T term for all samples. The residual electronic specific heat coefficient g increased with carrier density, and smoothly connected to the value of the non-superconducting sample. This behavior of g suggests a pair breaking mechanism that develops with doping. We tentatively attribute the origin of pair breaking to impurities, because their influence on d-wave superconductors increases when Tc, and hence the energy gap, decreases. The field dependence of g followed well the prediction for an impure d-wave superconductor.
63/65Cu NMR Study on Nd1.85Ce0.15CuO4+d
K Miyagawa, H Kawamura, K Kanoda, Y Onose, Y Taguchi, Y Tokura
Dept. of Appl. Phys., Univ. of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
The title material is known as the electron-doped high-TC superconductor, while the oxygenated sample is a semiconducting. The 63/65Cu NMR studies for a single crystal of oxygenated and reduced Nd1.85Ce0.15CuO4+d were performed. The NMR spectra of both samples show the single phase nature with small distribution in nQ. The NMR signal of the oxygenated sample disappeared around 150 K due to the magnetic ordering and below 30 K the signal was observed in a wide range of external filed. The line width of the reduced sample was narrower than that of the oxygenated sample but increased below 100 K. The electronic states of the oxygenated and reduced crystal are compared.
Coherent THz radiation from Tl-2212 thin films excited by optical laser pulse under magnetic field
Y. Tominaria, T. Kiwaa, H. Murakamia, M. Toniuchib, H. Waldc, P. Seidelc, H. Schneidewindd
aOsaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
bOsaka University and CREST/JST, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
cFriedrich-Schiller-Universitat, 07743 Jena, Germany
dDepartment of Cryoelectronics, P. O. Box 100239, D-07702 Jena, Germany
We observed resonant terahertz (THz) pulse radiation from Tl2Ba2CaCu2O8+d (Tl-2212) thin films by femtosecond optical pulse excitation under a radial magnetic field of ~ 100 Oe nearly parallel to the c-axis of the film. The observed waveform showed clear oscillations below 80 K. The frequency of the oscillations (630 GHz at 24 K) shifted to lower frequency region with increasing temperature as expected from Josephson Plasma phenomena.
ARPES Study on Electronic Evolution in Ca2-xNaxCuO2Cl2.
T. Sasagawaa, F. Ronningb, Y. Kohsakaa, M. Azumac, M. Takanoc, Z.-X. Shenb, H. Takagia
aDepartment of Advanced Materials Science, University of Tokyo, Bunkyo-ku, Tokyo 113-0033, Japan
bDepartment of Applied Physics and SSRL, Stanford University, Stanford, California 94305, USA
cInstitute for Chemical Research, Kyoto University, Uji, Kyoto-fu 611-0011, Japan
Electronic evolution from an antiferromagnetic insulator (AFI) to a high-Tc superconductor (HTS) was revealed by ARPES experiments on tetragonal Ca2-xNaxCuO2Cl2 single crystals, which were grown for the first time under high pressures ( £ 5.5 GPa). In an underdoped HTC (x = 0.1), we found clear fingerprints of the parent AFI: a shadow band and a large pseudo-gap. The results are most likely described by a ``chemical potential shift", which contrasts clearly with the ``pinned chemical potential" reported for the prototype La2-xSrxCuO4, demonstrating that the route to a HTS is not unique.
Superconducting transition in quasi-one-dimensional sulfide AXV6S8 (A=In,Tl) under magnetic field
Masahiro Suginoa, Toshiyuki Ueokaa, Yoshiko Fujiia, Tsukio Ohtanib, Minoru Yamaguchia
aDepartment of Applied Physics, Okayama University of Science, Ridai-cho, Okayama 700-0005, Japan
bLaboratory for Solid State Chemistry, Okayama University of Science, Ridai-cho, Okayama 700-0005, Japan
The superconducting phase transitions of quasi-one-dimensional compound(InV6S8,TlV6S8,V6S8)have been studied by the measurement of AC magnetic susceptibility c¢. The c¢ of powdered sample decreased stepwise, and was characterized by two transition temperatures TC1 and TC2. The TC1 is considered to be the transition temperature in the grains, and TC2 is the inter-grain transition temperature. Under the magnetic field, TC2 shifted to the lower temperature even in the small field(20G). In order to see the character of inter-grain phase transition, the third harmonic component of c¢ is measured.
Impossibility of superconducting state in multiwall carbon nanotubes
Anatoly I. Romanenkoa, Alexandr V. Okotruba, Lubov G. Bulushevaa, Olga B. Anikeevaa, Nikolai F. Yudanova, Cheng Dongb, Yongming Nib
aInstitute of Inorganic Chemistry Siberian Branch of Russian Academy of Science, Novosibirsk, Russia
bNational Laboratory for Superconductivity, Institute of Physics CAS, Beijing, China
Magnetic susceptibility c of pristine and brominated arc-produced sample of multiwall carbon nanotubes was measured from 4.2 to 400 K. It was shown that an additional contribution Delta c(T) to c(T) is dominated by quantum correction to c for interaction electrons (interaction effects-IE) at T below 50 K for both samples. The IE shows a crossover from two-dimensional to three-dimensional behaviors at B = 5.5 T. The effective interaction between electrons for interior layers of nanotubes is repulsive and the electron-electron interaction lc was estimated to be lc ~ 0.26 for pristine sample and did not change with bromination. This result shows that superconductivity is impossible in multiwall carbon nanotubes.
Palladium-hydrogen system as a possible room temperature superconductor
P. Tripodia, D. Di Gioacchinob
aENEA-Centro ricerche Frascati, Via Enrico Fermi 45, 00044 Frascati (Italy)
bI.N.F.N. Frascati National Laboratory, Via Enrico Fermi 40, 00044 Frascati (Italy)
A phenomenological description of resistivity (r), for high loaded (1:1) palladium-hydrogen (Pd-H) system at T=300K has been developed. Experimental data at 300K, show a r value less of the pure Pd and a Tc greater than 9K reported in literature. This approach uses a parallel model of two processes: i) r has a linear raising with the concentration (x=H/Pd), due to the increases of relative Pd lattice volume; ii) r as an exponential decreasing versus x, due to a superconducting fluctuation at very high x in Pd-H. At xc (xc(300K)=1.6) the superconducting state is produced. LTSC inverse isotopic effect for 0.6 £ x £ 0.96, changes in normal HTSC isotopic effect at x » 1.
Superconsuctivity and In-plane Resistivity in La2-xSrxCuO4
Jun'ya Hori, Shingo Iwata, Hiromi Kurisaki, Fumihiko Nakamura, Takashi Suzuki, Toshizo Fujita
Department of Quantum Matter, ADSM, Hiroshima University, Higashi-hiroshima, 739-8530, Japan
The correlation between the in-plane resistivity (rab) and the superconducting transition temperature (Tc) has been investigated in La2-xSrxCuO4 under anisotropic pressure up to 8.0 GPa. The pressure suppresses the orthorhombic distortion and stabilizes the tetragonal lattice which enhances the superconductivity. In the underdoped samples, the inter-layer compression brings about some kind of localization of rab at low temperatures. The collapse of two-dimensional (2D) metallic state probed by rab kills the superconductivity. On the other hand, the overdope boundary for the superconductivity is discussed in terms of the 2-3D crossover of the electronic state.
Thermal conductivity in HgBa2Ca4Cu5Oy (Hg-1245)
T. Watanabea c, K. Tokiwaa c, S. Itoa a, S. Mikusuaa, Y. Hashinakaaa, A. Iyobc, Y. Tanakabc
a Tokyo University of Science, Noda, Chiba, Japan
bAIST, Tsukuba, Ibaraki, Japan
cCREST, JST, Kawaguchi, Saitama, Japan
As the temperature is lowered below Tc (107K), a sharp increase in the thermal conductivity k, having a maximum at about 60K, is observed in this compound as shown in various cuprate superconductors. In this compound, however, a distinct features that the enhancement of k below Tc is comparatively broad and has some structure are noted. This behavior in k may be related to a special case of this compound in which there coexist a superconducting CuO2 planes and antiferromagnetic ordered CuO2 planes in the unit cell, indicated for the first time from the experiments of NMR and mSR3.
Dip Effect and Surface Barrier in Single Crystal YBa2Cu3Ox
J.W. Lina, H. Luob, Y. Liub, S.Y. Dingb
aCollege of Science, Hohai University, Nanjing 210098, P R China
bNational laboratory of Solid State Microstructures, Department of Physics, Nanjing University, Nanjing 210093, P R China
Measurement was made of ac susceptibility (acs) as a function of temperature T for a YBa2Cu3O6.993 single crystal at in dc fields (H). Dip effect was observed in the experimental ac susceptibility curves. By comparing the acs result with transport experiment in references, it is shown that the dip effect (DP) is in fact the second peak effect (SPE) of critical current density jc. It is also identified that the SPE in jc(H) is just the one observed in jc(T). Carefully measurement of acs in lower dc fields shows signal indicating the transition of flux pinning mechanism. We discussed the experimental in details.
Sequence of transitions from 2D to 3D superconductivity in YBa2Cu3O6+x
Zdenek Janua, Georgy Tsoyb, Miloslav Novakb
aJLTL, Charles University, V Holesovickach 2, 180 00 Prague 8, Czech Republic
bJLTL, Institute of Physics, ASCR, Na Slovance 2, 182 21 Prague 8, Czech Republic
Using high-resolution SQUID magnetometer we observed a sequence of transitions from 2D to 3D superconducting state on YBa2Cu3O6+x single-crystals. The transitions reflect the layered structure of material and clearly do not originate in non-homogeneous sample with multiple phases with varying Tc or vortex matter. While both transitions at temperature around 92 K have width only 10 mK and show sudden appearance of phase coherence in 2D CuO2 layers and CuO2-Y-CuO2 sandwiches, the third transition at temperature about 87 K reflects appearance of the weak coupling between sandwiches through the Ba-CuO-Ba barriers.
Effects of electron irradiation on the vortex order-disorder transition in La2-xSrxCuO4 crystals
Y. Radzynera, A. Shaulova, Y. Yeshuruna, K. Kishiob, S. Okayasuc
aInstitute of Superconductivity, Bar-Ilan University, Ramat-Gan 52900, Israel
bDepartment of Applied Chemistry, The University of Tokyo, Tokyo 113-8656, Japan.
cJAERI, 2-4 Shirakata Shirane, Tokai-mura, Naka-gun, Ibaraki 319-1195 Japan
The vortex order-disorder phase transition line in La0.937Sr0.063CuO4 exhibits a steep concave decrease throughout the whole temperature range. This unusual behavior is explained postulating that in La0.937Sr0.063CuO4, both thermal and disorder-induced fluctuations take part in destabilizing the vortex lattice. Irradiation of the samples with electrons causes a significant decrease in both the magnitude of the transition field and the curvature of the transition line. These results are interpreted as caused by the enhanced role of disorder-induced fluctuations as compared with thermal fluctuations.
Study of c-axis I-V Characteristics of Misaligned Tl-2212 Film
Guohua Zhanga, Sheng Luoa, Qingfei Shenb, Chunguang Lib, Rongtao Luc, Shaolin Yanc
aDepartment of Physics, University of Science and Technology, Beijing 100083, China
bNational Laboratory for Superconductivity & Institute of Physics, CAS, Beijing 100080, China
cDepartment of Electronics, Nankai University, Tianjin 300071, China
A 5 mm width micro-bridge was patterned on misaligned Tl-2212 film deposited on SrTiO3 substrate. The c-axis and in-plane I-V characteristics of the Tl-2212 micro-bridge have been measured in different temperatures and fields. The hysteretic I-V characteristics have RSJ like behavior, and can be well fitted if thermal fluctuations and interlayer capacitance are taken into account. The temperature dependence of the c-axis critical current can be well described by the Ambegaokar-Baratoff theory. The c-axis quasi-particle tunnelling I-V characteristics in different temperature show obvious scaling behavior as well as the in-plane I-V characteristics, which could be explained by existing flux dynamics models.
Vortex Phases in Single Crystals of Bi2Sr2CaCu2O8+d Near ab-plane Studied by c-axis and In-plane Resistivity Measurements
J. Mirkovi\'ca,b, S. Savel'eva, S. Hayamaa, E. Sugaharaa, K. Kadowakia
aInstitute of Materials Science, University of Tsukuba, Tsukuba 305-8573, Japan,
bFaculty of Sciences, University of Montenegro, Podgorica, Yugoslavia
Both the in-plane and out-of-plane resistivity measurements have probed the vortex lattice melting transition in the single crystals of Bi2Sr2CaCu2O8+d, indicating the crossing lattice structure in the wide angular and temperature ranges. However, the drastic difference in behavior was observed in magnetic fields applied close to the ab-plane, suggesting the complex melting transition of the vortex-lattice into the vortex-smectic phase, which, at higher temperatures, may melt into the vortex-liquid phase via the second-order phase transition. The observed behavior may be interpreted also as the possible indication of the transition from the crossing vortex-lattice to the tilted vortex-lattice near the ab-plane.
Suppression of Surface Barriers in Single Crystals of Bi2Sr2CaCu2O8+d by In-plane Magnetic Fields
J. Mirkovi\'ca,b, S. Savel'eva, K. Kadowakia
aInstitute of Materials Science, University of Tsukuba, Tsukuba 305-8573, Japan,
bFaculty of Sciences, University of Montenegro, PO Box 211, Podgorica, Yugoslavia
The in-plane resistivity measurements were performed on the several Bi2Sr2CaCu2O8+d single crystals, characterized by different electric contact geometries including the Corbino contact configuration, which discards the surface barriers. In the platelet samples, the non-linear behavior of resistivity was observed well above the vortex lattice melting transition in the vortex liquid phase, across a wide temperature range and magnetic fields applied along the c-axis. The resistance has been measured at the various magnetic field orientations, with the constant out-of-plane component. It was found that the in-plane magnetic fields strongly suppress the non-Ohmic behavior of resistivity, i.e., the surface barrier effect.
Local Permeability Studies of Vortex States in Bi2Sr2CaCu2O8+y under Tilted Fields
Takashi Murata, Masashi Tokunaga, Tsuyoshi Tamegai
Department of Applied Physics, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
In a strongly anisotropic superconductor Bi2Sr2CaCu2O8+y, vortices generated by tilted fields form two orthogonal lattices of pancake and Josephson vortices, i. e., crossing lattices. Owing to the attractive interactions between these two lattices, various forms of ground state can be realized. Some of the ground states in the crossing-lattices state have been reported by anomalies in irreversible magnetization and direct observations by scanning Hall probe microscopy. We apply local permeability measurements using a micro-Hall probe to explore the phase diagram and the nature of ground states of vortex solid at high temperatures and under tilted fields. In addition to the vortex-lattice melting transition, we find a clear step in the real part of permeability at fields with almost constant in-plane component.
Multiple components of the order parameter induced around the dx2-y2-wave vortex core
Mitsuaki Takigawa, Masanori Ichioka, Kazushige Machida
Department of Physics Okayama University Okayama 700-8530, Japan
On the basis of the Bogoliubov de Gennes theory for the two-dimensional extended Hubbard model, the vortex structure of dx2-y2-wave superconductors is analyzed. Multiple components of the order parameter are induced around the dx2-y2-wave vortex core: extended s-wave, px ±i py-wave components. The px+ipy-wave component has +2 winding at the core and -1 winding in the middle of nearest vortices, and the px-ipy-wave component has -1 winding in the middle of next nearest vortices. We also study these induced order parameters and the induced spin-triplet-dx2-y2-wave component when the antiferromagnetism(or checkerboard or stripe) is induced at the vortex core.
Ac Magnetic Flux Profile of Melt-textured Sm-Ba-Cu-O Superconductor
Kazuo Inoue, Masato Murakami
Superconductivity Research Laboratory, ISTEC, 1-16-25 Shibaura, Minato-ku, Tokyo, 105-0023, Japan
We have investigated the ac magnetic flux profile of melt-textured Sm-Ba-Cu-O superconductor using the ac inductive method. The ac penetration depth increases with increasing the dc magnetic field up to 0.75 T at 77 K. However, further increase up to 2.5 T leads to the decrease of the ac penetration depth. This suggests that the penetration of ac field is affected by the field-induced pinning due to the Sm-rich clusters.
Disorder Dependence of Vortex Core States in Bi2Sr2CaCu2Ox Studied by Low Temperature Scanning Tunneling Spectroscopy
Ken Matsubaa, Hideaki Sakataa, Takashi Mochikub, Kazuto Hiratab, Nobuhiko Nishidaa
aDepartment of Physics, Tokyo Institute of Technology, Ohokayama, Meguro-ku, Tokyo 152-8551, Japan
bNanomaterials Laboratory, National Institute for Materials Science, Sengen, Tsukuba, Ibaraki 305-0047, Japan
The vortex cores in underdoped Bi2Sr2CaCu2Ox have been measured at 6K in 8T by scanning tunneling spectroscopy. In these cores, we have observed the enhancement of the quasiparticle density of states at the energies of about ±9meV. The strength of the enhancement has been found to depend on the degree of microscopic disorder in the sample. The possible reason for the disorder dependence of the vortex core states will be discussed.
Dynamics of Vortex Motion in High-Tc Superconductor La1-xSrxCuO4
Minoru Sasakia, H. Iwasakib, A. Ohnishia, Y. Isobeb, N. Asakaa, M. Hayashib, H. Ebisawab
aDepartment of Physics, Yamagata Univ., Yamagata 990-8560, Japan
bH. I.: JAIST; Y. I.: Hiroshima Univ.; M. H. and H. E.: Tohoku Univ., Japan
Transient thermoelectric effect (TTE) and transient Nernst effect (TNE) have been measured for La0.86Sr0.14CuO4 crystals. The TTE and TNE signals closely related to vortex motion are observed; the former consists of two components with delay times of ms and ms, while the latter has merely slow one. We suppose that the fast and slow components result in the motions of free vortex and collective vortices, respectively.
Plastic vortex flow in current-driven disordered Josephson junction networks
Takaaki Kawaguchi
Department of Technology, Shimane University, 1060 Nishikawatsu, Matsue 690-8504, Japan
Current-driven dynamics of superconducting phases of Josephson junction networks (JJNs) in a magnetic field is studied using numerical simulations. For JJNs with positional disorder, plastic depinning of vortices occurs at a certain threshold current and then there appear plastic flow and elastic flow states with increasing current. For strong disorder we find that dynamics of the plastic flow is governed by a nucleation effect of vortex-antivortex pairs and then the threshold current of the plastic flow regime shows a certain scaling behavior. We discuss the scaling properties for some types of networks. In addition, from an analysis of phase coherence, we find that there appears a dynamical critical behavior in the plastic flow state. We discuss its universal aspects by comparison with other related phase models.
Nonlinear Response in the Vortex State of Unconventional Superconductors
Takanobu Jujo
Department of Physics, Kyoto University, Kyoto 606-8502
The magnetic field (H) dependence of the density of states in the vortex state of the unconventional superconductors is discussed. The Doppler-shifted quasiparticle spectrum seemingly explain the ÖH-dependence of the specific heat coefficient as Volovik ('93) showed. In this paper it is shown that the Doppler shift is invalid in the unconventional superconductors, and only the suppression of the amplitude of the superconducting gap can induces the finite density of states near the Fermi level as in the conventional (s-wave) superconductors. The invalidness of the Doppler shift originates from the neglect of the nonlocal effect. The nonlocal effect eliminates the nonanalytic dependence on the superfluid velocity of the local density of states and therefore the superfluid velocity cannot induce the finite density of states near the Fermi level. The thermal conductivity is also discussed based on this theory.
Measurement of AC Losses in Superconducting Tapes subjected to both AC Transport Current and Magnetic Field using a Bolometric technique
Massimiliano Polichettia, Yura Bugoslavskyb, David Caplinb
aDipartimento di Fisica, Universita' di Salerno and INFM, Via S. Allende, Baronissi (SA), I-84081, Italy
bImperial College, Blackett Laboratory, London SW7 2BZ, UK
AC losses have been measured on HTS tapes in presence of both AC current and AC magnetic field, by using an extended bolometric technique. Tapes as long as 10 cm are thermally anchored at its ends to the 77 K bath , and are placed in a chamber where the spurious effects due to thermal instabilities are strongly reduced. The AC power losses are rapidly obtained by measuring the resulting temperature gradient between the centre and the extremities of the sample, with a sensitivity of ~ 1 mW/cm. In this way, the losses can be measured at various frequencies, phases and amplitudes of the AC current (up to ~ 40A) and field (up to ~ 600 mT), which are in fact completely independent of each other.
Vortex dynamics in mesoscopic strips
Clécio C.S. Silva, Leonardo R.E. Cabral, J. Albino Aguiar
Departamento de Fisica, Universidade Federal de Pernambuco, 50670-901, Recife-PE, Brasil
Flux penetration and vortex patterns in narrow superconducting strips are studied. The edge barrier, vortex-vortex interactions, and the position dependent effective flux are calculated assuming the high-k limit and strip width x << W << L, where L is the effective penetration depth and x the coherence length. Vortex penetration and time-evolution inside the sample, as an external magnetic field is looped, are simulated by numerically solving the coupled Langevin equations of motion. The edge barrier shows to have an important role on the system dynamics and, in particular, on the commensurability effects in a regular array of columnar defects. We also simulate transport measurements for a current applied along the strip. The effects of quenched disorder are also discussed.
Vortex lattice structures in tetragonal BCS superconductors
Anton Knigavko, Frank Marsiglio
Department of Physics, University of Alberta, Edmonton, Canada T6G 2J1
We investigate vortex lattice structures of tetragonal BCS superconductors in the clean limit for the case H||c. Using recently developed by us expansion in the ``distance'' from the Hc2(T) curve 4 we are able to account for nonlocality of interactions in the vortex lattice and access a considerable portion of the superconducting region of T-H plane, far away from Tc. Anisotropies of Fermi surface and pairing s-wave interactions are assumed to be small and treated as perturbations. Application of the results to vortex lattice transformations 5 in borocarbide superconductors are discussed.
Theoretical Study on Vortex Lattices in Tetragonal Superconductors
Noriyuki Nakai, Predrag Miranovic, Masanori Ichioka, Kazushige Machida
Department of Physics, Okayama University, Okayama 700-8530, Japan
We investigate vortex lattices in tetragonal and cubic superconductors based on the quasiclassical theory. In these superconductors, the band structure has a fourfold symmetry depending on the crystal structure. Thus it is possible that a square vortex lattice becomes stable under a magnetic field. In borocarbides, the superconducting gap has an anisotropy. When the gap anisotropy has a fourfold symmetry, a square vortex lattice becomes stabilized in a high field. Each fourfold anisotropy of the gap and the band structure stabilizes two kinds of square vortex lattices. We consider two kinds of orientations of vortex lattices rotated by 45 degree from the other. We compare the free energy of four kinds of vortex lattices. The free energy is obtained by the self-consistent calculation solving Eilenberger equations numerically. We show the field and the temperature phase diagram of vortex lattices by this study.
Phase transition in vortex matter driven by bias current
Boris Ya. Shapiro, Moshe Gitterman, Irina Shapiro
Physics Department,Bar-Ilan University, 52100 Ramat Gan,Israel
The phase transition in vortex matter subjected to external magnetic field and bias current are described by the generalized Ginzburg-Landau equations with additional convective and effective field terms. Analytical and numerical solutions of this equation provide the interface between ordered and disordered vortex phases. The location of this interface boundary depends nonmonotonically on the strength of a bias current. We predict a sudden extention of the disordered vortex state across the entire sample at some critical value of the bias current.
Specific Heat of the Spin-Triplet Superconductor Sr2RuO4 with Nonmagnetic Impurities
Naoki Kikugawaa, Yoshiteru Maenob
aVenture Business Laboratory and Department of Physics, Kyoto University, Kyoto 606-8501, Japan
bInternational Innovation Center and Department of Physics, Kyoto University, Kyoto 606-8501, Japan
We report the substitution effect of nonmagnetic Ti4+ for Ru4+ on the specific heat of Sr2Ru1-xTixO4 from x = 0 (spin-triplet superconductor) to 0.09 (magnetically ordered phase with glassy behavior) via magnetic instability point at xc ~ 0.025. We found that specific heat divided by temperature CP/T around xc deviates from the conventional Fermi-liquid behavior seen in pure Sr2RuO4 and shows the logarithmic behavior at xc. Such critical enhancement is attributable to the diverging two-dimensional antiferromagnetic fluctuation, which arises mainly from the nesting within one of the Fermi-surface sheets.
Field dependence of Vortex structure in px ±ipy-wave superconductors
Masanori Ichioka, Kenji Shiroyama, Kazushige Machida
Department of Physics, Okayama University, Okayama 700-8530, Japan
To understand the vortex states in Sr2RuO4, we investigate differences of the vortex structure for two chiral pairings px ±ipy. We calculate the pair potential, the internal field, the local density of states, and free energy in the vortex lattice state based on the quasiclassical Eilenberger theory, and analyze the magnetic field dependence. The induced opposite chiral component of the pair potential plays an important role in the vortex structure. It produces ÖH-behavior of the zero-energy density of states at higher field. We also calculate the vortex structure based on the Ginzburg-Landau theory, and discuss the transition from px +ipy-wave superconducting domain to stable px -ipy-wave superconducting domain under magnetic field.
Theory of Superconducting Mechanism and Gap Structure of Sr2RuO4
Takuji Nomura, Kosaku Yamada
Department of Physics, Kyoto University, Kyoto 606-8502, Japan
We discuss a superconducting mechanism and gap structure of the spin-triplet superconductor Sr2RuO4 on the basis of the three-band repulsive Hubbard model. The effective pairing interaction is derived within the third order perturbation for the on-site Coulomb energy, and the transition temperature is estimated by solving the Éliashberg equation. Here we take into account the full momentum-frequency dependences of the order parameter. As a result, we may conclude that the spin-triplet superconductivity is a natural result of electron correlations. The derived order parameter possesses the anisotropic p-wave symmetry, and take the maximum value on the main band g. We are planning to analyse the experimental results of physical quantities including specific heat below Tc, and investigate the consistency of the theoretical in-plane gap anisotropy with the experimental results, following the elementary BCS theory.
Coreless vortices in p-wave superconductors
Boris Ya. Shapiroa, Baruch Rosensteinb, Irina Shapiroa
aPhysics Department,Bar-Ilan University, 52100 Ramat Gan,Israel
bElectrophysics Department,National Chiao Tung University, Hsinchu 30043,Taiwan
Simulations of a three component time dependent Ginzburg-Landau (Abelian Higgs) model reveals that the dominant topological defects are vector vortices rather than conventional Abrikosov (Nielsen-Olesen) vortices or skyrmions. We describe in detail these vortices in the steady state and discuss their possible role in the dynamics. In particular we conclude that the vector vortices have a superconducting core distinct from the superconducting bulk state. The profile of the vector order parameter and the magnetic field are calculated.
Non-saturating upper critical field of organic superconductor
k-(BEDT-TTF)2Cu[N(CN)2]Cl
T. Ishiguroa, Y. Shimojoa, H. Yamochib, G. Saitob
aPhysics Department, Kyoto University, Kyoto 606-8502, Japan
bChemistry Department, Kyoto University, Kyoto 606-8502, Japan
The upper critical field of the organic superconductor k-(BEDT-TTF)2Cu[N(CN)2]Cl shows non-saturating behavior toward 0 K under the magnetic field applied strictly parallel to the superonducting plane. The inclination angle dependence of the upper critical field from the plane is discussed in terms of the interplay between the orbital pair-breaking effect and the Pauli paramagnetic effect in addition to vortex dynamics. The relation to the spatially modulated order-parameter state predicted by Fulde-Ferrell and Larkin-Ovchinnikov is argued.
Vortex Lattice Anisotropy in Conducting Plane in Organic Superconductors
L. Ya. Vinnikova, T. L. Barkova, M. V. Kartsovnika, N. D. Kushchb
aInstitute of Solid State Physics, RAS, 142432 Chernogolovka, Moscow district, Russia
bInstitute of Problems of Chemical Physics, RAS, 142432 Chernogolovka, Moscow district, Russia
Vortex structure in organic superconductors k-(BEDT-TTF)2CuN(CN)2Br (for the first time) and k-(BEDT-TTF)2Cu(NCS)2 has been investigated by using decoration technique at the magnetic fields region up to 23 Oe. Quantitative analysis of high quality vortex lattice (VL) images shows the VL anisotropy which can be treated as a penetration depth anisotropy. Mutual orientation of vortex and crystal lattices is discussed.
Development of AC susceptibility technique under high pressure and its application to organic superconductor
Akio Kuritaa, Masashi Miyashitaa, Hiromi Taniguchia, Kazuhiko Satoha, Masashi Tamurab, Reizou Katob, Masato Hedoc, Yoshiya Uwatokoc
aDepartment of Physics, Saitama University, Saitama,Saitama, 338-8570, Japan
bRiken, Wako, Saitama, 351-0198, Japan
cThe Institute for Solid State Physics, University of Tokyo, Kashiwa, Chiba, 277-8581
The pressure-temperature phase diagram is one of the most important information for unraveling the mechanism of the organic superconductors. Then we developed an experimental technique that made the measurement of AC susceptibility under high pressure up to 35kbar possible. In the present work, we investigated bulkly nature of the organic superconductor, k-(BEDT-TTF)2Cu[N(CN)2]Br, under pressure.
How to determine pairing symmetry of quasi-1D organic superconductors through magneto-tunneling spectroscopy
Y. Tanumaa, K. Kurokib, Y. Tanakac, R. Aritad, S. Kashiwayae, H. Aokid
aGraduate School of Natural Science and Technology, Okayama University, Okayama, 700-8530, Japan
bDepartment of Applied Physics and Chemistry, The University of Electro-Communications, Chofu, Tokyo 182-858, Japan
cDepartment of Applied Physics, Nagoya University, Nagoya 464-8063, Japan
dDepartment of Physics, University of Tokyo, Hongo, Tokyo 113-0033, Japan
eNational Institute of Advanced Industrial Science and Technology, Tsukuba, 305-8568, Japan
We propose that pairing symmetry of quasi-1D superconductors (TMTSF)2X can be experimentally identified from tunneling spectroscopy in the presence of magnetic field, where the effect of magnetic field is treated in terms of the Doppler shift.
Tunneling spectroscopy of superconducting Li0.48(THF)0.3HfNCl
Toshikazu Ekinoa, Tomoaki Takasakib, Hironobu Fujiia, Shoji Yamanakac
aFaculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 739-8521, Japan
bGraduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima 739-8526, Japan
cGraduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan
Tunneling measurements on the electron-doped layered superconductor Li0.48(THF)0.3HfNCl (THF;C4H8O) with Tc » 26K have been carried out. Science the surface of this compound is very reactive, we have employed in situ break junction to obtain unaffected junction interface. The result shows the gap value of 2D » 9 - 11 meV. This leads to the gap ratio 2D/kBTc up to ~ 5, which is much larger than the BCS value.
Anomalous Quasiparticle Excitations in Y(Ni1-xPtx)2B2C
K. Ohishia, K. Kakutaa, J. Akimitsua, A. Kodab, W. Higemotob, R. Kadonob, J. E. Sonierc, A. N. Priced, R. I. Millerd, R. F. Kiefld, M. Noharae, H. Suzukie, H. Takagie
aDept. of Phys., Aoyama-Gakuin Univ., Setagaya-ku, Tokyo 157-8572, Japan
bIMSS, High Energy Accelerator Research Organization (KEK), Ibaraki 305-0801, Japan
cDept. of Phys., Simon Fraser Univ., Burnaby, British Columbia, Canada V5A156
dTRIUMF and Dept. of Phys., Univ. of British Columbia, Vancouver, British Columbia, Canada V6T1Z1
eGraduate School of Frontier Sciences, Univ. of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan
The magnetic field distribution in the vortex state of Y(Ni1-xPtx)2B2C has been probed by mSR. At low fields the vortex core radius rv (H) in x = 0 sample decreases with increasing H much steeper than what is expected from the ÖH behavior of the Sommerfeld constant g(H), strongly suggesting that the anomaly in g(H) primarily arises from the quasiparticle excitations outside the vortex cores.
Upper critical field and critical current anisotropy in RNi2B2C thin films
Stuart C. Wimbush, Ludwig Schultz, Bernhard Holzapfel
IFW Dresden, PO Box 270016, 01171 Dresden, Germany
Orientation-dependent measurements of superconducting properties such as the upper critical field Hc2 and the critical current density Jc have been performed on epitaxial thin films of the non-magnetic borocarbide compound YNi2B2C and the magnetic HoNi2B2C. These quantities are seen to vary in a highly anisotropic manner both out-of-plane and within the basal plane of the borocarbide unit cell, presenting a complex behaviour partly in agreement with and partly contradicting that reported for bulk samples. Comparison of the form of the anisotropy for the different properties and comparison between the measurements on the magnetic and non-magnetic sample allow conclusions to be drawn regarding the physical origin of the anisotropies.
H-T Phase Diagram and Magnetic Structure in ErNi211B2C
Haruko Takeshitaa, Michiyo Ochiaib, Emi Habutaa, Takashi Nagatab, Hazuki Kawano-Furukawab,c, Nobuo Furukawad, Hiroyuki Takeyae, Hideki Yoshizawaf, Kazuo Kadowakig
aG.S.H.S., Ochanomizu Univ., Bunkyo-ku, Tokyo 112-8610, Japan
bDept. of Physics, Ochanomizu Univ., Bunkyo-ku, Tokyo 112-8610, Japan
cPREST JST, Kawaguchi-shi, Saitama 332-0012, Japan
dDept. of Physics, Aoyama Gakuin Univ., Setagaya-ku, Tokyo 157-8572, Japan
eNIMS, Tsukuba-shi, Ibaraki 305-0047, Japan
fI.S.S.P., Univ. of Tokyo, Kashiwa-shi, Chiba 277-8581, Japan
gInstitute of Materials Science, Univ. of Tsukuba, Tsukuba-shi, Ibaraki 305-8573, Japan
By magnetization and neutron scattering measurements, we studied a weak ferromagnetic superconductor ErNi211B2C. We are going to present the best fit models of magnetic structure and H-T phase diagram.
A new infrared excitation in semiconducting Ba1-xKxBiO3 single crystals
Javed Ahmad, Taichiro Nishio , Hiromoto Uwe
Institute of materials science, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan
We report optical reflectivity measurements on Ba1-xKxBiO3 (x = 0, 0.15) single crystals in the frequency range 70-30000 cm-1 and at different temperatures in an attempt to understand the transport mechanism in the semiconducting phase before it undergoes semiconductor-metal transition. For x = 0.15, we find a new peak (peak3) in e2, in addition to already reported two peaks (peak 1 and peak 2), at around 1280 cm-1 (at 400 K). The peak 1 is attributed to an excitation across charge density wave energy gap of Bi 6s electrons from Bi3+ to Bi5+ and that of peak 2 is from Bi4+ to Bi5+. We notice, with temperature increasing from 50 K to 400 K, the spectral weight of (i) peak 3 increases, (ii) optical phonons decreases, (iii) total ir transition shifts towards higher frequency. The results are explained in terms of a new excitation of small polarons taking in to account the strong Bi 6s electrons-phonon interaction.
Evidence for high temperature superconducting phases in Pd-H system
P. Tripodia, D. Di Gioacchinob, R. Borellia, D. Vinkoc
aENEA-Centro ricerche Frascati, Via Enrico Fermi 45, 00044 Frascati (Italy)
bI.N.F.N. Frascati National Laboratory, Via Enrico Fermi 40, 00044 Frascati (Italy)
cHERA S.r.l. Hydrogen Energy Research Agency, Corso della Repubblica 448 , 00049 Velletri (Italy)
New superconducting phases with high Tc have been found in the palladium-hydrogen (Pd-H) system, in addition to well-known low Tc for this material. Infact as reported in literature, the Tc of Pd-H is a function of x=H/Pd, when the 0.6 £ x £ 0.96 the Tc is in 0K £ Tc £ 9K range. Resistance measurements of Pd-H system with the stoichiometric ratio, x ³ 0.96, versus temperature in a DC magnetic field have been done. These measurements show a critical temperature Tc ranges of: 30K £ Tc £ 60K. Moreover, superconducting phases up to Tc=273K probably occur when the x ³ 1. A critical superconducting current density of 6*104A/cm2 has been measured at 77K with HDC=0T.
1E. D. Bauer et al.: Phys. Rev. B 65 (2002) 100506(R).
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3 K.Tokiwa et al., The 23th LT Conference 2002.
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